IES: Institute of Enviromental Sciences. A professional organization
dedicated to the promotion of technology in several different areas. The
Contamination Control Division of the Association has written several
Recommended Practices for HEPA and associated filters and equipment.

Impingement: The process in which particles are removed from an
airstream because of their inertia. As air containing a particle, flows toward a
filter fibre or other collecting surface, the particle does not follow the air
streamlines because of its inertia. Instead it moves in a straight line
colliding with the filter fibre or surface to which it may become attached.

Inertia: The tendency of a body in motion to move in the same straight
line unless acted upon by some external force.

Infiltration: The controlled or uncontrolled leakage of air into a
conditioned space.

Inorganic: Molecules whose chemical structure do not contain carbon.

Interception: The process in which a particle is removed from an
airstream as it follows the streamilnes around a fiber. The particle comes in
contact with a fiber and stays attached to it because the attractive forces
between the fibre and the particle are stronger than the forces of disruption of
the moving airstream.